title: Trends and characteristics of animal-vehicle collisions in the United States.
abstract: BACKGROUND
  Since 1990, fatal animal-vehicle collisions (AVCs) in the United States have more than doubled. This paper examines annual AVC trends in the United States over a 19-year period, seasonal and diurnal patterns of AVC risk, the geographic distribution of crash risk by state, and the association between posted speed limit and AVC crash risk in darkness.
  
  
  METHODS
  AVCs were compiled from the Fatality Analysis Reporting System (FARS) and the General Estimates System (GES) for the years 1990-2008 to examine annual crash trends for fatal and nonfatal crashes. Seasonal trends for fatal AVCs were examined with the aggregated FARS dataset; seasonal trends for fatal and nonfatal AVCs were also examined by aggregating four years of Michigan crash data. State-by-state distributions of fatal AVCs were also described with the aggregated FARS dataset. Finally, the relationship between posted speed limit and the odds that a fatal or nonfatal AVC occurred in darkness were examined with logistic regressions using the aggregated FARS and Michigan datasets.
  
  
  RESULTS
  Between 1990 and 2008, fatal AVCs increased by 104% and by 1.3 crashes per trillion vehicle miles travelled per year. Although not all AVCs involve deer, daily and seasonal AVC crash trends follow the general activity pattern of deer populations, consistent with prior reports. The odds that a fatal AVC occurred in darkness were also found to increase by 2.3% for each mile-per-hour increase in speed; a similar, albeit smaller, effect was also observed in the aggregated Michigan dataset, among nonfatal crashes.
  
  
  CONCLUSIONS
  AVCs represent a small but increasing share of crashes in the United States. Seasonal and daily variation in the pattern of AVCs seem to follow variation in deer exposure and ambient light level. Finally, the relative risk that a fatal and nonfatal AVC occurred in darkness is influenced by posted speed limit, suggesting that a driver's limited forward vision at night plays a role in AVCs, as it does in pedestrian collisions.
  
  
  CONCLUSIONS
  The association between speed limit and crash risk in darkness suggests that AVC risk might be reduced with countermeasures that improve a driver's forward view of the road.
authors.affiliation: University of Michigan Transportation Research Institute, 2901 Baxter Rd., Ann Arbor, MI 48109-2150, USA. jsully@umich.edu
authors.forename: John M
authors.initials: JM
authors.lastname: Sullivan
mesh_terms: D000063:Accidents, Traffic / Q000401:mortality / Q000706:statistics & numerical data* / Q000639:trends; D000818:Animals; D001336:Automobiles / Q000706:statistics & numerical data*; D002940:Circadian Rhythm / Q000502:physiology; D016001:Confidence Intervals; D003624:Darkness; D003670:Deer; D005843:Geography; D006801:Humans; D008027:Light; D016015:Logistic Models; D008824:Michigan; D012306:Risk; D012621:Seasons; D013997:Time Factors; D014785:Vision, Ocular; D014794:Visual Fields / Q000502:physiology*